Aledo (u-LEE-doh) is a city in Mercer County, Illinois, United States. The population was 3,640 at the 2010 census, up from 3,613 in 2000. It is the county seat of Mercer County.
Aledo was established in the 1850s when the railroad was extended to that point. It was briefly named DeSoto, after Hernando de Soto, until the discovery of an identically named village in Jackson County, Illinois. Development in the Downtown Aledo Historic District began in the 1850s, and the oldest surviving buildings date from the following decade. A post office has been in operation at Aledo since September 24, 1856. In 1857, the county seat was moved to Aledo from Millersburg after a countywide referendum. Aledo was incorporated on August 15, 1863. In the 1950s, the first Tastee-Freez in the United States was built in the downtown.
Aledo is located at 41°12′1″N 90°45′0″W (41.200172, -90.749956).
According to the 2010 census, Aledo has a total area of 2.392 square miles (6.20 km2), of which 2.38 square miles (6.16 km2) (or 99.5%) is land and 0.012 square miles (0.03 km2) (or 0.5%) is water.
As of the census of 2010, there were 3,640 people, 1,568 households, and 947 families residing in the city. The racial makeup of the city was 98.5% (3,586) white; 0.6% (22) African American; 0.0% (1) Native American; 0.3% (12) Asian; 0.1% (4) from other races; and 0.4% (15) from two or more races.